Aqueous Solutions Flashcards
What is it meant by the “Forward reaction” in two way reactions?
When reactants collide and react to produce products.
What is it meant by the “Reverse reaction” in two way reactions?
When the products react to form the original reactants. For example, tearing down a lego house would be a reverse reaction as it results in the original building blocks.
What symbol do we give two way reactions?
A double arrow
What is dynamic equilibrium?
The state reached when the rate of reactants and products being produced is the same, therefore there is no overall change in reactant or product concentrations. For example If someone was building a lego house at the same rate as another was tearing the same lego house apart, there would be no changes in the size of the lego house.
Do you need to have equal amounts of reactants and products to reach equilibrium?
No, Equilibrium is reached when the rates of the reactants and products are the same. For example a child building a lego house may start building before his friend decides to start tearing it apart, therefore the child building it has had the chance to already make the lego house at a reasonable size.
What is it meant by the position of equilibrium?
How much product was made in comparison to how much reactant was left over at the point when the reaction reached equilibrium
What is the symbol used for the equilibrium constant?
Kc
What does the equilibrium constant tell us?
The amount of reactants compared to the amount or products at equilibrium. Ratio/proportion.
How to calculate the equilibrium constant?
Products/Reactants. E.g 1A + 2B - 3C + 4D would be
Kc = [C]3 + [D]4 / [A]1 + [B]2
In the equation for equilibrium constant (Kc = [C]3 + [D]4 / [A]1 + [B]2) what do the square brackets refer to?
Concentration of the molecules at the time of equilibrium. eg [C] would be the concentration of molecule C
What happens to the numbers in front of the reactants and products in the chemical equation when calculating the equilibrium constant?
They become exponents in the equilibrium constant equation.
Can solids and liquids be used when calculating the equilibrium constant?
No, we will leave these out. Instead only include molecules which have the (aq) brackets . Gases may sometimes be included.
What is important about temperature when calculating the equilibrium constant?
Kc is specific for a particular temperature. Therefore when calculating, state the temperature. As If the reaction is done at a different temperature the proportion of products and reactants will likely be different resulting in a different position of equilibrium.
What does the value calculated from the equilibrium constant equation tell you?
It is an indication of the more dominant/favoured reaction.
What would a very small Kc (less than 0.001) indicate?
That there are a lot more reactants than products, therefore this would tell us that equilibrium favoured the reverse reaction.
What would a very large Kc (More than 1000) indicate?
That there were a lot more products than reactants therefore this would tell us the equilibrium favoured the forward reaction.
What does a Kc value of 1 indicate?
That the concentration of productions and reactants is equal. Also any value between 0.001 and 1000 is close enough to be considered equal. Indicating that no particular reaction direction was favoured over the other.
What is the job of Qc?
To tell us the proportion of products to reactants before equilibrium is reached. By calculating this value we will know whether the reaction has reached equilibrium, this happens when Qc = Kc.
How do we know whether a reaction has reached equilibrium using the formula for Qc?
The value of Qc will = the value of Kc. If these values are different either the forward or reverse reaction will be favoured until Qc = Kc.
What formula does Qc use?
The same as Kc. Products/Reactants
How does a reaction reach equilibrium if Qc is smaller than Kc ?
The concentration of products will increase while the concentration of reactants will decrease. Therefore the forward reaction will be favoured until equilibrium is reached.
How does a reaction reach equilibrium if Qc is larger than Kc
The concentration of reactants will increase while the concentration of products will increase. Therefore the reverse reaction will be favoured until equilibrium is reached.
What is the name for Qc?
Reaction Quotient
What is the difference between the equilibrium constant Kc and the reaction quotient Qc?
Kc tells us the proportion of products to reactants at equilibrium, Qc tells us the proportion of products to reactants before equilibrium is reached or can be an indicator that equilibrium has been reached if its value equals the value of Kc.
When is equilibrium reached in two way reactions?
When the concentrations of both products and reactants are the same therefore there are no overall changes in the reaction.
What does le châtelier’s principle state?
If an equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract this change. Essentially what this means is that whatever is done to change equilibrium the system will do the opposite to revert it back to a state of equilibrium.
What is a real life example of le châtelier’s principle?
When your body temperature gets too high the body sweats to cool the body down.
After changing the conditions of a reaction/system in equilibrium, when it returns back to equilibrium, wills its position and Kc value be the same?
Unlikely.
If you change the concentration of a system in equilibrium, for example you add more reactants, how will the system respond.
Following le châtelier’s principle the system will use the forward reaction to counteract the change, therefore balancing the proportions again.
If you change the concentration of a system in equilibrium, for example you add more products, how will the system respond.
Following le châtelier’s principle the system will use the reverse reaction to counteract the change, therefore balancing the proportions again.
What is pressure when dealing with chemistry?
The force per area exerted by one object against another. In chemistry terms, the force caused by gas molecules being confined.
How do you change the pressure of a system in equilibrium?
Option 1: Concentration: Gas molecules flow aimlessly exerting force when hitting other objects in its system. For example, the more gas molecules in a system the more likely molecules are to collide and exert force, therefore, more force is exerted and the pressure is increased.
Option 2: Volume/size of the system: Changing the volume/size of the system changes how much pressure is in the system, for example, decreasing the volume/size will give the molecules less room to move therefore a higher chance of colliding and exerting force therefore pressure is increased.
What is an endothermic reaction?
When heat energy is absorbed or transfered into the system from its surroundings. This is because the products need to have more energy than the reactants resulting in colder surroundings.
What is an exothermic reaction?
When heat energy is released or transferred from the system to its surroundings. This is because the reactants need to have more energy than the products resulting in warmer surroundings.
True or False? In two way reactions both reactions must be exothermic or they both must be endothermic.
False, In two way reactions they must be different. For example if the forward reaction is endothermic the reverse reaction must be exothermic.
When the temperature increases what reaction is favoured?
Endothermic reaction.
When the temperature decreases what reaction is favoured?
Exothermic reaction.
What are catalysts?
They increase the reaction rate of a whole chemical reaction.
What do catalysts do equally with two way reactions in equilibrium?
They increase the reaction rate of both the forward and reverse reaction equally. Therefore products and reactants are being produced faster than before, therefore they have no effect on the position of equilibrium.
